The present invention relates to an oxygen absorbent package using a microporous film or nonwoven fabric as at last part of material constituting the package.
Oxygen absorbents are widely used to keep oxygen out of the atmosphere in which foods and other products that do not like oxygen are stored. But if oxygen absorbents are used in connection with the storage of moist products and materials constituting the package packing oxygen absorbents are water permeable, the moisture enters the interior of the package of the absorbent and aqueous slurry of oxygen absorbent is formed. The aqueous slurry oozes out of the package and smears the foodstuffs.
Active research and development efforts have recently been made on thin plastic films such as microporous films and nonwoven sheets. Since these thin plastic films are as highly air-permeable as paper, they can be used as a material for packaging oxygen absorbents. However, this film is usually made of a single layer of polyolefin such as polyethylene and polypropylene, so it is difficult to heat-seal the microporous film by means of conventional packaging machines. The reason is that when two sheets of mono-layer films are adhered by melting inside portions of the mono-layer film, melted film is adhered to heat-seal bars or heat rolls of machine. A special heat-sealer, such as an impulse heat-sealer is necessary in order to heat-seal mono-layer film. When such special heat sealer is used in automatic packaging machines in order to heat-seal the mono-layer film, it is impossible to operate the automatic packaging machine at a high speed. So, when the mono-layer film is heat-sealed by an impulse heat-sealer, a decrease in efficiency is unavoidable. In addition, a microporous film is weakened. So a microporous film is not practical as a packaging material for packing an oxygen absorbent.
Oxygen absorbent packages using a plastic nonwoven sheet are disclosed in several prior art references. For example, Japanese Patent Publication (Kohkai) No. 2164/81 discloses a composite package including at least two layers, i.e. the plastic nonwoven sheet and an oxygen permeable but water-impermeable layer. But this package has the nonwoven sheet laminated or coated with a thermoplastic synthetic resin to reduce the inherent high gas permeability of the nonwoven sheet, so if the oxygen absorbent is put in the package, the desired oxygen removal rate is not obtained.